Discontinuous ply for runflat tire construction

ABSTRACT

The innermost carcass ply of a runflat tire ( 50 ) having a radial carcass ply is a discontinuous ply ( 52 ) that includes two portions ( 52   a   , 52   b ) each disposed within one of the sidewalls ( 43, 45 ). In one embodiment, each of the two discontinuous ply portions is composed of two layers ( 64, 66 ) of cross-biased cords ( 65, 67 ) which are disposed between the two wedge inserts ( 58   b   , 59   b ) in each sidewall. In another embodiment, the two portions ( 72   a   , 72   b ) of the discontinuous ply ( 72 ) are composed of wavy metal cords. In a third embodiment, a runflat tire incorporating either embodiment of the discontinuous ply ( 92   a   , 92   b ) is built using the locked, tie-in construction for the carcass ply.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional application of U.S. application Ser. No. 09/889,248having a filing date of Jul. 11, 2001 now U.S. Pat. No. 6,712,108 and acommon assignee with present application.

TECHNICAL FIELD

The present invention relates to the construction of pneumatic radialply runflat tires and particularly to a ply component of the tire.

BACKGROUND OF THE INVENTION

Various methods have been devised for enabling the safe continuedoperation of unpressurized or underpressurized vehicle tires with theintent of minimizing further damage to the uninflated tire and withoutsimultaneously compromising vehicle handling over a distance from theplace where the tire has lost its pressure to a place desired by thedriver, such as a service station, where the tire can be changed. Lossof tire pressure can, of course, result from a variety of causes,including puncture by a foreign object such as a nail or other sharpobject piercing the pneumatic tire installed on a vehicle.

Pneumatic tires designed for sustained operation under conditions of nopressure or underpressurization are also called runflat tires, as theyare capable of being driven, or “running,” while uninflated, or in whatis generally called a “flat” condition.

The conventional pneumatic tire, when uninflated, collapses upon itselfwhen it is carrying the wheel loading of a vehicle. The tire's sidewallsbuckle outward in the region where the tread contacts the ground, makingthe tire “flat.”

Runflat tires are also called extended mobility tires, the latter phrasebeing compressed to EMT, which is a term of art. A tire designed forrunflat or EMT operation is designed such that the tire structure alone,and in particular the structure of the sidewalls, has sufficientstrength and rigidity to support the vehicle's wheel load and provideadequate vehicle handling when the tire is not inflated. The sidewallsand internal surfaces of EMT tires do not collapse or buckle ontothemselves. Such tires do not typically contain or use other supportingstructures or devices to prevent the collapse into a flattened conditiondue to loss of tire pressure.

Among the many examples of runflat tires is a tire described in U.S.Pat. No. 4,111,249, entitled the “Banded Tire,” in which a hoop orannular band, approximately as wide as the tread, is circumferentiallydeployed beneath the tread. The hoop in combination with the rest of thetire structure could support the vehicle weight in the uninflatedcondition.

Another approach toward EMT or runflat technology has been simply tostrengthen the sidewalls by increasing their cross-sectional thickness.That is, runflat tires incorporate sidewalls that are thicker and/orstiffer so that the tire's load can be carried by an uninflated tirewith minimum adverse effects upon the tire itself and upon vehiclehandling until such reasonable time as the tire can be repaired orreplaced. However, due to the large amounts of rubber required tostiffen the sidewall members, cyclical flexural heating during runflatoperation becomes a major factor in tire failure. This is especially sowhen the uninflated tire is operated for high speeds and the cyclicalflexure rate is correspondingly high. Pirelli discloses an example of arunflat tire design having thickened sidewalls in European Pat. Pub. No.0-475-258A1.

Typical methods used in sidewall thickening and stiffening include theincorporation of circumferentially disposed “wedge inserts” within theconcave inner peripheral surface of the sidewall portion of the carcass,which is the region in the tire usually having the lowest resistance todeformation under vertical loading. The wedge inserts, which are oftenreferred to simply as inserts, are usually crescent shaped incross-sectional views. The incorporation of one or more wedge insertswithin each sidewall of a tire thickens the sidewalls substantially.Sidewall thickness in the region between the bead and the tread shoulderis often nearly uniform, when viewed in cross section.

U.S. Pat. No. 5,368,082, by Oare et al, having a common assignee,discloses a low-aspect-ratio, runflat pneumatic radial ply tire whichemploys wedge inserts in the sidewalls. Approximately six additionalpounds of weight per tire was required to support an 800 lb load in thisuninflated tire. This invention, although superior to prior attempts atrunflat tire design, imposed a weight penalty. Fortunately, that weightpenalty could be offset by the elimination of a spare tire and the tirejack. However, this weight penalty becomes even more problematic in thedesign of tires having higher aspect ratios and in tires designed forhigh performance.

U.S. Pat. Nos. 5,427,166 and 5,511,599 to Walter L. Willard, Jr.,disclose the addition of a third ply and the addition of a third insertin the sidewall of a runflat tire to theoretically further increase therunflat performance of the tire over that of the U.S. Pat. No.5,368,182. The Willard patents discuss some of the load relationshipsthat occur in the uninflated condition of the tire and demonstrate thatthe Oare et al. concept can be applied to additional numbers of pliesand inserts.

In general, runflat tire design is predicated upon the installation ofreinforcing inserts inside each sidewall flex area. The inserts in eachsidewall, in combination with the plies, add rigidity to the sidewallsin the absence of air pressure during runflat operation. The U.S. Pat.No. 5,368,082 teaches a sidewall construction for runflat tires in whichthe tire is constructed with two plies, an inner liner and tworeinforcing wedge inserts in each sidewall. The two inserts in eachsidewall are disposed such that one insert is located between the twoplies while the other insert is located between the inner liner and thefirst or innermost ply.

While the high resistance to compression deflection of the insertsprovides the necessary resistance to the collapse of the uninflatedloaded tire, the use of multiple plies and more than one reinforcingwedge insert in each sidewall has drawbacks which include the abovementioned increase in tire weight and flexure-induced heat build up.Such designs also increase the tire's complexity in ways that adverselyaffect manufacturing operations and quality control.

U.S. Pat. No. 4,287,924, by Deck et al, places a two part reinforcingwedge inside the carcass which is described as: “a support member (20)of lenticular section, made of an elastomer and extending from thevicinity of the beads (12) to below the edges of the belt . . . [and]constituted by two parts with different flexibility . . . . ” In orderto promote evacuation of the heat produced in the thick part of thesupporting shaped parts (20), means are provided which consist of aheat-conducting sheet or layer (28) embedded in the body of shaped parts(20) and extending at least to the vicinity of beads (12). Preferablythe layer extends over the whole height of shaped parts (20), from theupper part of the side walls adjacent to the belt of crown (23) to thevicinity of the beads. The layer (28) is advantageously disposed betweenthe two parts of shaped part (20), and can be constituted for example byflexible parallel metallic cords extending along the radial planes ofthe tire.

European Patent Application No. EP 0 822 105 A2, by Walter et al(Michelin), comprises a plurality of crescent-shaped reinforcing members(5) and a plurality of carcass layers (6), and provides first and secondpartial carcass layers (62, 64) along with a filler rubber portion (24)and a second crescent-shaped reinforcing member (56). In the Walterapplication's FIG. 4, it can be determined that the placement ofelements in the sidewall, from the inside out, is: innerliner (44),first crescent-shaped reinforcing member (54), inner carcass layer (68),second crescent-shaped reinforcing member (56), first partial carcasslayer (62), filler rubber portion (24), second partial carcass layer(64), and outer sidewall (42). The filler rubber portion is placed abovethe bead similar to an apex. FIG. 6 shows a variation with a differentshaped filler rubber portion (24 a), but still places the wedges (54,56) on either side of the inner carcass layer, and places the partialcarcass layers (62, 64) axially outside of the [complete] carcass layer(68). The partial carcass layers extend from the vicinity of the bead upunder the crown region to a specified distance (L1) axially inside ofthe edge of the tread belt. As best it can be determined, the partialcarcass layers are comprised of standard carcass ply materials.

In summary, the goals in runflat tire design are to provide a low-cost,light-weight tires that give good runflat vehicle handling as well asgood service life during runflat operation. Accordingly, theconsiderations that must be taken into account in runflat tire designinclude the use of minimal additional material to the tire (to achievethe desired sidewall stiffness) as well as minimal additional steps inthe manufacturing process.

Among the design considerations for EMT or runflat technology is thenature of the sidewall loading and corresponding stresses that ariseduring runflat operation. For example, during runflat operation, theinsert-reinforced sidewalls still undergo an outward or axial buckling(though not to the extreme extent of an uninflated non-runflat tire) inthe region adjacent to where the tire's tread makes contact with theroad. Such “loading” of the sidewalls causes them to deform in such away that the outermost portions of the sidewalls, including especiallythe outermost carcass plies, experience tensile stresses. At the sametime, the innermost portions of the insert-reinforced sidewalls, e.g.,the portions of each wedge insert that lie closest to the tire'sinnerliner, experience large increases in compressive stresses. Thiscombination of tensile and compressive stresses is also cyclical as thetire rotates. It follows that as the vehicle moves faster, the rate offlexural heat buildup increases.

OBJECTS OF THE INVENTION

It is an object of the present invention to provide a runflat radialtire as defined in one or more of the appended claims and, as such,having the capability of being constructed to accomplish one or more ofthe following subsidiary objects.

One object of the present invention is to provide a runflat radial tirehaving a minimum number of components and requiring fewer manufacturingsteps than prior art designs.

One object of the present invention is to provide a runflat radial tirehaving a minimum number of components and requiring fewer manufacturingsteps than prior art designs.

Another object of the present invention is to provide a runflat radialtire having a simplified ply structure that reduces the overall tireweight.

Another object of the present invention is to provide a runflat radialtire whose simplified manufacturing sequence allows for improvedmanufacturing quality control.

Yet another object of the present invention is to provide a runflat tirehaving good normal inflation handling characteristics as well as goodrunflat handling properties and runflat operational service life.

Still another object of the present invention is to apply the inventiveconcept to a variety of alternative tire sizes and aspect ratios.

SUMMARY OF THE INVENTION

The present invention relates to a pneumatic radial ply runflat tirehaving a tread, a carcass comprising a radial ply structure, a beltstructure located between the tread and the radial ply structure, andtwo sidewalls each reinforced by two wedge inserts. Each sidewallcontains one portion each of a two-part discontinuous ply disposedbetween the wedge inserts in each sidewall. Each of the two portions ofthe two-part discontinuous ply of the present invention is made from twolayers of cross-biased fabric. Each of the layers comprisesparallel-aligned cords made from materials from the class of materialsthat contains nylon and rayon. The parallel-aligned cords of therespective fabric layers are each oriented at an angle with respect tothe radial direction that is more or less equal in magnitude butopposite in direction, making angles with respect to the radialdirection that are preferably between 40 degrees and 65 degrees and mostpreferably at angles with respect to the radial direction of 45 degreesand 55 degrees.

In another embodiment, each portion of the two-part, discontinuous plyor semi-ply of the present invention is made from a single layer ofmetal cords that are wavy with respect to the radial direction. Themetal cords are preferably made of steel.

In yet another embodiment, the two-part, discontinuous ply invention, ineither of the two constructions generally described above, isincorporated in a tire built according to the locked tie-in constructionmethod.

BRIEF DESCRIPTION OF THE DRAWINGS

The structure, operation, and advantages of the invention will becomefurther apparent upon consideration of the following description takenin conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a prior art runflat tire designincorporating two wedge inserts in each sidewall and two plies in theply structure;

FIG. 2 is a cross-sectional view of a tire containing the presentinvention;

FIG. 3 is a cross-sectional view of a two-layer non-metallic fabricreinforced ply according to a first embodiment of the invention;

FIG. 4 shows the orientation of the reinforcing cords in the view of theembodiment shown in FIG. 3;

FIG. 5 is a cross-sectional view of a metal reinforced ply according toa second embodiment of the invention;

FIG. 6 shows the structure of the metal reinforcing cords that areincorporated in the embodiment shown in FIG. 5; and

FIG. 7 is a cross-sectional view of an embodiment of the invention inwhich the tire's main carcass ply employs the locked tie-in constructionmethod.

DEFINITIONS

“Apex” refers to an elastomeric filler located radially above the beadcore and between the plies and the turnup plies.

“Aspect ratio” means the ratio of the section height of a tire to itssection width; also refers to the cross-sectional profile of the tire; alow-profile tire, for example, has a low aspect ratio.

“Axial” and “axially” means the lines or directions that are parallel tothe axis of rotation of the tire.

“Bead” or “bead core” generally means that part of the tire comprisingan annular tensile member of radially inner beads that are associatedwith holding the tire to the rim; the beads being wrapped by ply cordsand shaped, with or without other reinforcement elements such asflippers, chippers, apexes or fillers, toe guards and chafers.

“Belt structure” or “reinforcement belts” or “belt package” means atleast two annular layers or plies of parallel cords, woven or unwoven,underlying the tread, unanchored to the bead, and having both left andright cord angles in the range from 18° to 30° relative to theequatorial plane of the tire.

“Breakers” or “tire breakers” means the same as belt or belt structureor reinforcement belts.

“Carcass” means the tire structure apart from the belt structure, tread,undertread over the plies and the sidewalls, but including the beads,plies, and, in the case of EMT or runflat tires, the wedge insertssidewall reinforcements.

“Casing” means the carcass, belt structure, beads, sidewalls and allother components of the tire excepting the tread and undertread.

“Circumferential” most often means circular lines or directionsextending along the perimeter of the surface of the annular treadperpendicular to the axial direction; it can also refer to the directionof the sets of adjacent circular curves whose radii define the axialcurvature of the tread, as viewed in cross section.

“Cord” means one of the reinforcement strands, including fibers or metalor fabric, with which the plies and belts are reinforced.

“Crown” or “tire crown” means the tread, tread shoulders and theimmediately adjacent portions of the sidewalls.

“Equatorial plane” means the plane perpendicular to the tire's axis ofrotation and passing through the center of its tread; or the planecontaining the circumferential centerline of the tread.

“Footprint” means the contact patch or area of contact of the tire treadwith a flat surface at zero speed and under normal load and pressure.

“Gauge” refers to thickness.

“Inner liner” means the layer or layers of elastomer or other materialthat form the inside surface of a tubeless tire and that contain theinflating fluid within the tire.

“Insert” means the crescent- or wedge-shaped reinforcement typicallyused to reinforce the sidewalls of runflat-type tires; it also refers tothe elastomeric non-crescent-shaped insert that underlies the tread; itis also called a “wedge insert.”

“Lateral” means a direction parallel to the axial direction.

“Normal inflation pressure” means the specific design inflation pressureat a specified load assigned by the appropriate standards organizationfor the service condition for the tire.

“Normal load” means the specific design inflation pressure and loadassigned by the appropriate standards organization for the servicecondition for the tire.

“Ply” means a cord-reinforced layer of rubber-coated radially deployedor otherwise parallel cords.

“Radial” and “radially” mean directions radially toward or away from theaxis of rotation of the tire.

“Radial ply structure” means the one or more carcass plies or which atleast one ply has reinforcing cords oriented at an angle of between 65°and 90° with respect to the equatorial plane of the tire.

“Radial ply tire” means a belted or circumferentially-restrictedpneumatic tire in which at least one ply has cords which extend frombead to bead are laid at cord angles between 65° and 90° with respect tothe equatorial plane of the tire.

“Section height” means the radial distance from the nominal rim diameterto the outer diameter of the tire at its equatorial plane.

“Section width” means the maximum linear distance parallel to the axisof the tire and between the exterior of its sidewalls when and after ithas been inflated at normal pressure for 24 hours, but unloaded,excluding elevations of the sidewalls due to labeling, decoration orprotective bands.

“Shoulder” means the upper portion of sidewall just below the treadedge.

“Sidewall” means that portion of a tire between the tread and the bead.

“Tangential” and “tangentially” refer to segments of circular curvesthat intersect at a point through which can be drawn a single line thatis mutually tangential to both circular segments.

“Toe guard” refers to the circumferentially deployed elastomericrim-contacting portion of the tire axially inward of each bead.

“Tread cap” refers to the tread and the underlying material into whichthe tread pattern is molded.

“Tread width” means the arc length of the tread surface in the planeincludes the axis of rotation of the tire.

“Wedge insert” means the same as “insert.”

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Prior Art Embodiment

With reference to FIG. 1, a cross-sectional view of a typical prior art,pneumatic radial runflat tire 10. The tire 10 has a tread 12, sidewalls16, 18, a belt structure 14 comprising belts 24, 26, a fabric overlay 28disposed between the tread and the belt structure, bead regions 20 a, 20b, and a carcass structure 22. The carcass structure 22 comprises afirst ply 30 and a second ply 32, a gas-impervious inner liner 34, apair of beads 36 a, 36 b, a pair of bead filler apexes 38 a, 38 b, afirst pair of crescent-shaped sidewall wedge inserts 40 a, 40 b, and asecond pair of sidewall wedge inserts 42 a, 42 b. The first or innermostwedge inserts 40 a, 40 b are located between the inner liner 34 and thefirst ply 30, and the second wedge inserts 42 a, 42 b are locatedbetween the first ply 30 and second ply 32. The reinforced sidewallportions 16, 18 of carcass structure 22 give the tire 10 runflatcapability.

The generalized prior art runflat tire 10 shown in FIG. 1 illustratesthe structural reinforcements in the sidewall area of a two-ply carcassdesign. Other runflat or EMT designs employ a single ply carcassstructure. They also might use a single wedge-insert reinforcementwithin each sidewall, disposed between the inner liner and the singleply. In other two-ply EMT designs, a single wedge insert might bedisposed within each sidewall between the two plies. Prior art runflatdesigns even include three-ply tires having three wedge inserts withineach sidewall, as mentioned above in the Background of the Invention.

As can be seen in FIG. 1, the use of the wedge inserts 40 a, 40 b, 42 a,and 42 b substantially increases the thickness of the sidewall portions16, 18 as compared to comparable non-runflat tires. The sidewalls 16, 18have more or less uniform thickness between in the bead regions 20 a, 20b and the lateral most portions of the tread 12. This generalized priorart runflat tire design exemplifies the thickened sidewalls thatcharacterize EMT or runflat tire designs. When the tire 10 isuninflated, the insert-reinforced sidewalls 16, 18 support the tire'sload with minimal deflection. Such runflat tire designs provide goodvehicle handling and performance under conditions of full inflation, andthey provide acceptable runflat vehicle handling and runflat operationallife when the tire is underinflated or uninflated. Runflat tiresgenerally weigh more than equivalent non-runflat-capable tires, due tothe reinforcing material used in the sidewall wedge inserts.Furthermore, the greater structural complexity of runflat tiresadversely influences manufacturing time and quality control.

When the prior art tire 10 shown in FIG. 1 is operated in a condition oflow to zero inflation pressure, the portions of the sidewalls that areclosest to where the tread makes contact with the ground becomedeflected outward axially. In non-runflat designs, this same sort ofoutward or axial deflection of the sidewalls also takes place, ofcourse, but to such an extreme degree that the vehicle cannot becontrolled when the tire loses pressure. The tire can even come off therim, due to the extreme deformation of the carcass. In runflat designs,the axial deflection of the sidewalls adjacent to the ground-contactingportion of the tread is minimized by the thick, wedge-insert reinforced,sidewalls. Those skilled in the art will recognize that such axialdeformation of the sidewalls gives rise to a combination of tensile andcompressive stresses within the sidewalls. More specifically, theoutermost portion of each sidewall experiences tensile stresses whilethe inner regions undergo compression stresses. Those skilled in the artwill further recognize that the thicker the reinforced sidewalls are,the lower will be the maximum respective tensile and compressivestresses. However, the use of such thicker sidewall reinforcements alsomakes the tire heavier.

Accordingly, one way to reduce the weight of a runflat tire is to modifythe design of the type of two-ply runflat design shown in FIG. 1. Theinner ply 30, which is also known as the first ply (a nomenclature whichfollows the sequence in which the components of the tire are assembled),separates the innermost inserts 40 a, 40 b from the outermost inserts 42a, 42 b. Within the sidewalls regions 16, 18, the first ply 30 isdisposed in such a way between the respective wedge inserts as to beexposed primarily and almost exclusively to cyclical compressivestresses during normal operation but most especially during runflatoperation when sidewall flexing magnitudes are maximum. It is the secondply 32 that bears the tensile stresses associated with deformation ofthe sidewalls 16, 18.

The exposure of the first ply 30 to compressive stresses during runflatoperation of the tire, and the precise location of the first ply inrelation to the respective insert reinforcements 40 a, 40 b, 42 a and 42b, works in such a way as to enhance the combined stiffness of the wedgeinserts in each sidewall. In other words, the disposition of the ply 30between the respective wedge inserts 40 a, 40 b, 42 a, and 42 b in eachsidewall gives the two wedge inserts in each sidewall a greaterresistance to deformation than were the ply 30 does not separate the twowedge inserts in each sidewall. The net effect, therefore, of the ply 30being disposed between the respective wedge inserts allows for a runflattire design in which the total weight of the two inserts in eachsidewall can be less than the corresponding weight of a single largeinsert affording an equivalent stiffening effect to the sidewalls of arunflat tire design.

An Embodiment of the Present Invention

Recognizing the above described benefits of the ply 30 disposed betweenthe respective inserts 40 a, 40 b, 42 a, and 42 b within each sidewallof the prior art runflat tire depicted in FIG. 1, the present inventionseeks to achieve a reduction of tire weight and a simplification of thetire's design and construction complexity by eliminating the portion ofthe first ply that underlies the tread 12.

FIG. 2 shows a cross-sectional view of a tire 50 incorporating oneembodiment of the two-part discontinuous ply or semi-ply of the presentinvention. The two-part semi-ply, or discontinuous ply 52 is defined bytwo portions 52 a, 52 b, each of which is disposed in the flex region ofa sidewall 43, 45, respectively, of the tire 50. The tire 50 has a tread48, sidewalls 43, 45, bead regions 56 a, 56 b, and a carcass structurewhich comprises a discontinuous inner first ply 52 and an outer secondply 57, a gas-impervious innerliner 44, a pair of beads 49 a, 49 b, apair of bead filler apexes 51 a, 51 b, a first pair of crescent-shapedsidewall wedge inserts 58 a, 58 b, and a second pair of sidewall wedgeinserts 59 a, 59 b. The first or innermost wedge inserts 58 a, 58 b arelocated between the inner liner 44 and the discontinuous first ply 52,and the second wedge inserts 59 a, 59 b are located between thediscontinuous first ply 52 and second ply 57. In FIG. 2, the semi-plyportion 52 a extends from the radially inwardmost position 55 a to theradially outwardmost position 53 a in sidewall 43, while the semi-plyportion 52 b is a mirror-image version of semi-ply portion 52 a insidewall 45. The two ply portions 52 a, 52 b constitute the totaldiscontinuous ply 52 that replaces the first ply 30 of the prior arttire 10 shown in FIG. 1.

FIG. 3 shows a cross-sectional view of one sidewall 45 of the tire 50shown in FIG. 2. The two-layer, semi-ply portion 52 b comprises an outerfabric layer 60 b and an inner fabric layer 62 b. An inner wedge insert58 b is separated from an outer wedge insert 59 b by the semi-plyportion 52 b. The semi-ply portion 52 b extends radially outward fromthe location 55 b near or in the bead region 56 b to a location 53 bnear the shoulder 54 b of the sidewall 45 of the tire 50. In otherwords, the semi-ply portion 52 b and its counterpart 52 a (in FIG. 2)are disposed in the flex area of the sidewalls 45, 43, respectively, ofthe tire 50 shown in FIG. 2.

In FIG. 3, the discontinuous or semi-ply portion 52 b separates thefirst wedge insert 58 b from the second wedge insert 59 b in such a wayas to afford the sidewall 45 the same stiffening benefit provided by thecorresponding part of the first ply 30 in the prior art tire 10 shown inFIG. 1. However, since the semi-ply portion 52 b in FIG. 3 is notcontiguous with its mirror-image counterpart, semi-ply portion 52 a inthe opposite sidewall 43 on the other side of the tire, a reduction inthe weight of the tire 50 is thereby gained. In other words, the weightreduction afforded by the present invention comes about from theelimination of that portion of the prior art first ply (30 in FIG. 1)which extends across the tire's crown portion beneath the tread 12 ofthe tire 10. The incorporation of such semi-ply portions 52 a, 52 b, asshown in FIGS. 2 and 3, contributes to the combined reinforcing rigidityof each sidewall 43, 45 as brought about primarily by the use of twowedge inserts 58 a, 58 b, 59 a and 59 b shown in FIG. 2.

The discontinuous ply portion 52 b illustrated in FIG. 3 comprises twofabric layers 60 b, 62 b, each of which comprises parallel-alignedfibers or cords made of materials from the class of materials thatincludes nylon and rayon. FIG. 4 shows the fabric layers 64, 66 andtheir respective parallel-aligned cords 65, 67. The parallel-alignedcords 65, 67 have respective bias angles β and α, as shown in FIG. 4.The bias angles β and α are measured with respect to the radialdirection and they are approximately equal in magnitude. The angles βand α are preferably between 40 degrees and 65 degrees relative to theradial direction, and most preferably between 45 degrees and 55 degrees.Below 40 degrees, the parallel aligned ends 65, 67 are not able toadequately withstand the compression generated on the sidewalls andshoulders and thereby can allow the cords to buckle because they do notremain in the tension mode. Alternatively, we do not want to exceed 65degrees because of limitations in the manufacturing process. In otherwords, the bias angles of the parallel-aligned cords 65, 67 of fabriclayers 64, 66, respectively, are oriented at crossed bias angles thatare more or less equal in magnitude with respect to the radialdirection, but opposite in direction, as shown in FIG. 4.

The two fabric layers 60 b, 62 b shown in FIG. 3 are encapsulatedbetween the two rubber wedge inserts 58 b, 59 b. Thus located, thediscontinuous ply 52 (FIG. 2) contributes compression stiffness to thetwo wedge inserts of the sidewalls 43, 45 shown in FIG. 2. The increasedbending stiffness thus afforded to the sidewalls gives the tire runflatmobility with reduced sidewall bending deflection. Overall tire weightis also reduced compared to the typical prior art tire 10 shown in FIG.1.

Alternative Embodiment

An alternative embodiment of the two-part discontinuous ply of thepresent invention is shown in the sidewall 70 shown in a cross-sectionalview in FIG. 5. The discontinuous inner or first ply 72 of thealternative embodiment includes a ply portion 72 b between a firstsidewall wedge insert 78 b and a second sidewall wedge insert 79 b, alllocated inside a second, outer carcass ply 77 in the sidewall flex areawhich extends approximately from the location 75 b near the bead region76 b to the approximate location 73 b near the shoulder 74 b. However,instead of being made of crossed-biased fabric layers as shown in FIGS.2 and 3, this alternative embodiment of the discontinuous ply portion 72b (and its unshown counter part in the opposite sidewall) consists of alayer 80 of steel or fabric cords 81, as shown in FIG. 6, that areparallel to each other and wavy with respect to the radial direction.The waviness of the layer 80 is defined by the angles γ and θ having arange of between 50 degrees and 100 degrees. The cords can beconstructed of metal or fabric and preferably of steel.

The waviness of the cords 81 minimizes the potential for buckling asthey are subjected to the compressive stresses associated with runflatoperation of a tire incorporating this embodiment of the discontinuousply of the present invention. In other words, if the cords 81 were notwavy and were oriented at a low angle relative to the radial direction,the cords would be more prone to buckling during runflat operation. Suchbuckling of parallel-aligned, radially oriented cords would contributeto the potential for separation of the cords from the adjacent rubber,an effect that could shorten the runflat operational service life of thetire.

As compared with the fabric concept of the first embodiment of thepresent invention, as shown in FIGS. 3 and 4, the wavy cord reinforcing,two-part discontinuous ply 72 depicted in FIGS. 5 and 6 has twoadditional benefits. First, the overall thickness of the sidewall 70(and its unshown mirror-image counterpart on the other side of the tire)can be less than the corresponding thickness of the sidewall 45 of thetire 50 shown in FIGS. 2 and 3 incorporating the crossed-bias fabricversion 52 a, 52 b of the discontinuous semi-ply invention. Second,whereas the crossed-bias fabric discontinuous ply 52 a, 52 b requiresthe inclusion of four components during construction of the tire (i.e.,two fabric layers in each sidewall), the cord embodiment 80 (shown inFIG. 6) of the two-part discontinuous ply 72 requires the inclusion ofonly two semi-ply portions, one in each sidewall, which simplifies themanufacturing and subsequent quality control processes. Third, the wavycord embodiment can weigh less than the embodiment shown in FIGS. 3 and4.

The respective embodiments shown in FIGS. 3 and 4 and in FIGS. 5 and 6are both applicable to mono-ply carcasses in which the single continuoussecond ply 57, 77 can be reinforced with more or less radially orientedfibers or cords made of either organic fibers or metal. FIGS. 3 and 5show the two embodiments of the invention within respective sidewallportions 45 and 70 wherein the respective continuous mono-ply segments57 and 77 are built according to the standard construction whereinrespective apexes 51 b and 71 b (and their unshown mirror imagecounterparts) are included near the respective bead regions 56 b and 76b.

Locked Tie-in Construction

FIG. 7 shows an embodiment of the invention in which a tire sidewallregion 90 is built according to the locked tie-in method ofconstruction. In the locked tie-in construction method, the singlecontinuous ply 97 wraps around the bead 96 b (and its counterpart,unshown) in such a way that the apexes 51 a, 51 b, 71 b of the other twoembodiments, shown in FIGS. 2, 3, and 5 are effectively eliminated fromthe bead region 93 b. That is, the turn-up end 97 b (and itscounterpart, unshown on the other side of the tire) of the continuouscarcass ply 97 are assembled in such a way as to make the turn-up ends97 b more or less contiguous with the main structural portion of ply 97,which extends between bead regions 93 b, of the continuous carcass ply97. The free end 101 b of ply turn-up end 97 b extends from a locationabove the bead 96 b upward to the mid-height of the sidewall 90. In thisembodiment, the discontinuous ply portion 92 b (and its unshowncounterpart) is, as in the previous embodiments, disposed radiallyacross the sidewall flex area of the sidewall 90 between a firstsidewall wedge insert 98 b and a second sidewall wedge insert 99 b, alllocated inside a second, outer carcass ply 97. The discontinuous ply 92b shown in FIG. 7 can be of the fabric type displayed in FIGS. 2, 3 and4, or the wavy cord type displayed in FIGS. 5 and 6.

The Invention in Relationship to Specific Prior Art

U.S. Pat. No. 5,435,370 ('370), to Ahmad et al., entitled “PneumaticTire Having Discontinuous Outer Carcass Ply,” discloses a pneumatic tirehaving a “second ply in continuous contact with the inner ply has twosection disposed such that the second ply is discontinuous orinterrupted in the crown area.” One significant difference between thedisclosure of the '370 patent and the present invention is that theprior art tire is not designed for runflat service. Additionally, thediscontinuous ply disclosed in the '370 patent is the second oroutermost ply, whereas in the present invention the two-partdiscontinuous ply is the first or innermost ply, and the two plies of'370 are in “continuous contact” with one another. Also, in the presentinvention, each of the two parts of the discontinuous semi-ply isdesigned to resist compressive stresses, while the respective two partsof the discontinuous carcass ply of '370 is disposed in a region exposedto tensile stresses in the portions of the sidewalls (adjacent to theportion of the tread that makes contact with the ground) that cannoteffectively resist compressive stresses and therefore buckles outwardduring normal inflated service and, especially, when the tire isuninflated.

patent application Ser. No. PCT/US98/20567, entitled, “ImprovedConstruction for Runflat Tire,” and having a common assignee with thepresent invention, discloses a runflat tire design having a single wedgeinsert in each sidewall of a tire having one or more carcass plies, bothof which are disposed outward of the single wedge insert in eachsidewall. Accordingly, the present invention might actually be construedto disclose a runflat tire design in which each the two wedge insertswithin each sidewall are tantamount to a single reinforced wedge insertin each sidewall, equivalent to, for example, the incorporation of fiberfiller in the single wedge insert. However, an important difference isthat each of the two discontinuous semi-plies of the present inventionexperiences and undergoes the same stresses and strains as areencountered in the sidewall regions by the first ply 30, shown in FIG.1, which separates the sets of double inserts, 40 a, 42 a, 40 b and 42 bin the generalized prior art runflat tire shown in FIG. 1. In otherwords, each of the two parts of the discontinuous semi-ply of thepresent invention performs precisely the same sidewall reinforcingfunctions as does the first ply 30 of the generalized prior art runflattire depicted in FIG. 1, but with the benefits described above.

While the invention has been described in combination with embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art in light of theforegoing teachings. Accordingly, the invention is intended to embraceall such alternatives, modifications and variations as fall within thespirit and scope of the appended claims.

1. A pneumatic radial ply runflat tire having a tread; two sidewallswith shoulders; a carcass comprising one or more outer radial carcassplies, two bead regions each containing an inextensible annular bead, aninnerliner, a two-part discontinuous ply with one portion contained ineach sidewall and disposed between two wedge inserts of substantiallyequal flexibility; and one or more belts located between the tread andthe outer radial carcass ply, the tire comprising; each combination oftwo wedge inserts with the portion of the two-part discontinuous ply isin a sidewall flex area located axially between the one or more outerradial carcass plies and the innerliner, and extending radiallyapproximately from a location near the bead region to an approximatelocation near the shoulder; each of the two portions of the two-partdiscontinuous ply is made from two layers of cross-biased fabric; eachof the cross-biased fabric layers is made of parallel-aligned cords; theparallel-aligned cords of a first fabric layer are oriented at an anglewith respect to the radial direction that is approximately equal inmagnitude but opposite in direction to the parallel-aligned cords of asecond fabric layer of the two layers of cross-biased fabric; and theparallel-aligned cords of the respective fabric layers are oriented atangles of between 40 degrees and 65 degrees with respect to the radialdirection.
 2. The tire of claim 1 characterized in that: the parallelcords are made of metal.
 3. The tire of claim 2, characterized in that:the parallel cords are made of steel.
 4. The tire of claim 1,characterized in that: the parallel cords are made of fabric.
 5. Thetire of claim 1 characterized in that: the parallel-aligned cords of therespective fabric layers are made of materials from the class ofmaterials that includes nylon and rayon.
 6. The tire of claim 1characterized in that: each of the two portions of the two-partdiscontinuous ply is made from one or more layers of parallel cordswhich are wavy with respect to the radial direction such that theparallel cords of each of the one or more layers are defined by anglesthat are between 50 degrees and 100 degrees.
 7. The tire of claim 6,characterized in that: the parallel cords are made of metal.
 8. The tireof claim 1 characterized in that: turn-up ends of the outer radialcarcass ply are substantially contiguous with the main structuralportion of the outer radial carcass ply; and the free ends of the plyturn up ends extend from above the corresponding bead upward to themid-height of the sidewall.
 9. A pneumatic radial ply runflat tirehaving a tread; two sidewalls with shoulders; a carcass comprising oneor more outer radial carcass plies, two bead regions each containing aninextensible annular bead, an innerliner, a two-part discontinuous plywith one portion contained in each sidewall and disposed between twowedge inserts of substantially equal flexibility; and one or more beltslocated between the tread and the outer radial carcass ply, the tirecomprising; each combination of two wedge inserts with the portion ofthe two-part discontinuous ply is in a sidewall flex area locatedaxially between the one or more outer radial carcass plies and theinnerliner, and extending radially approximately from a location nearthe bead region to an approximate location near the shoulder; each ofthe two portions of the two-part discontinuous ply is made from twolayers of cross-biased fabric; each of the cross-biased fabric layers ismade of parallel-aligned cords; the parallel-aligned cords of a firstfabric layer are oriented at an angle with respect to the radialdirection that is approximately equal in magnitude but opposite indirection to the parallel-aligned cords of a second fabric layer of thetwo layers of cross-biased fabric; and the parallel-aligned cords of therespective fabric layers are preferably oriented at angles of betweenabout 45 and 55 degrees with respect to the radial direction.